Actually, China sent only a labour corp, not an expeditionary force in WWI. The British, even after winning in North Africa, would not move to China because they're absence in Europe could lead to either a Nazi victory or a Soviet takeover of Europe, both harmful to they're interests. Plus that Stalin kept insisting about the opening of a second front and the Allies decision to let him deal with Hitler alone might even push him to a separate peace. Also, manpower was the least problem of the United Chinese Front as they outnumbered the Japanese by more than 4 to 1. They could maybe sent some Shermans, some Churchills and focus they're B-17s and later B-29s raids on the Chinese front. Also, as
@wiking said, Chang had some unresolved scores with Mao and while they're settlement could be postponed by the Soviet's need for the Western Allies to finish Hitler what would the Chinese gain by dying in Italy, France and Germany? You also have to consider that Chang was anti-imperialist and would not want his soldiers to be the "Westerners lambs for slaughter", especially as he already had a permanent seat secured in the future UN Security Council, so what could he gain more? Also, you have to consider that in WWI Japan didn't send troops to the Western Front for the same reason.